/in/foo.c: In function 'main':
/in/foo.c:5:6: warning: implicit declaration of function 'printrf' [-Wimplicit-function-declaration]
      printrf("Hello, World!");
      ^~~~~~~
/tmp/ccpDZZq0.o: In function `main':
foo.c:(.text.startup+0xe): undefined reference to `printrf'
collect2: error: ld returned 1 exit status